Select Geophysical Methods and Groundwater Modeling: Examples from USGS studies Claudia Faunt and a cast of others Current Preliminary Studies Stanford Water in the West Groundwater Data Workshop Series: Geophysical Methods for Sustainable Groundwater Management October 13, 2016
Geophysical Methods and Groundwater Models Define Geologic Framework Model Model Layers Hydraulic Properties Water levels and storage Observations for Calibration Subsidence Water Levels Water Quality Seawater Intrusion Example Studies Los Angeles, CA Death Valley, CA and NV San Pedro, AZ Ft. Irwin, CA Various desert basins, CA Central Valley, CA
Los Angeles Basin Sequence Stratigraphic and Groundwater Flow Model Dan Ponti and Scott Paulinski ~700 square miles of LA and parts of Orange County Objective: Increase understanding of artificial recharge, pumping, and other effects on LA groundwater (including seawater intrusion) -Drilled more than 50 multicompletion monitoring wells A A
3-D Sequencestratigraphic Model 13 sequences with complex faulting Data sources include: Seismic lines Borehole geophysical logs Water level, chemistry, and pumping data A A A A
New studies by the U.S. Geological Survey and its cooperators show that the geology of the Los Angeles Basin is much more complex than originally conceived. A seismic profile from the Port of Long Beach (D) shows the complex geology of the area. The sediment layers, shown as different colors, provide many potential pathways for saltwater intrusion. By understanding this geology, scientists can better determine where and how fast water moves within the various beds of sediment both onshore and offshore.
3-D Sequence-stratigraphic Model Study area heavily folded and faulted Layers pinch out Connections between different layers across faults Direct input to MODFLOW-USG (unstructured grid) Unstructured grid flexibility used to handle Layer pinch-outs Flow between layers across faults Faults as barriers to flow
Death Valley So. Amargosa Wayne Belcher, Don Sweetkind, Rick Blakely, Vicki Langenheim, Claudia Faunt, and others Fault definition -Basin-fill deposits -Basement Depth to basement Basin-fill lithologies
Basement based on gravity
Faults/ Structures Volcanic Rock extent Aeromagnetics augmented with TOM Magnetic Anomalies
Gravity surface, structures from gravity and magnetics, and model layers
San Pedro, AZ modeling and geophysics Jesse Dickinson Analyze lithology and geophysical logs to characterize bedrock, finegrained, and coarse-grained sediments Gravity models to identify depth to denser bedrock underlying the basin fill sediments Airborne and surface TEM surveys to map fine- and coarse-grained sediments Classify hydrogeologic units (HGUs) based on Well log lithology Field measurements of geophysical properties of basin fill sediments Develop 3D relations of the HGUs in the hydrogeologic framework model
Data for constructing framework model Gravity Determine depth to bedrock and aquifer thickness
Data for constructing framework model Surface Transient Electromagnetic (TEM) surveys Identify changes in electrical resistivity in the subsurface Low resistivity related to clay and silt High resistivity related to bedrock
Data for constructing framework model Aerial Transient Electromagnetic (TEM) Surveys Aircraft and transmitter Electromagnetic surveys - GEOTEM Map subsurface electrical properties Aquifer is electrically conductive Silt and clay conducts electricity better than sand and gravel Bedrock is not electrically conductive Receiver birds
Resistivity, HGUs, and model layering along E-W section
Ft. Irwin National Training Center, CA Jill Densmore, Lyndsey Ball, Geoff Cromwell, and Linda Woolfenden Airborne Electromagnetic Modeling (AEM) Resistivity maps at particular depths Gravity 10 miles Resistivity cross sections along flight lines Granite Saline playa lake 30 miles Metamorphic rocks
Gravity-defined depth-to-basement AEM + Gravity-defined depth-to-basement 5 km A A B B C C A B C South Dacite Dome Resistivity (ohm-m) 5 km 1000 100 10 Gravity-defined basement + AEM basement 500 m North
Translation between basin fill resistivity and hydraulic conductivity Few wells = limited ability to develop resistivity-k relations Resistivity zones used to develop geologically realistic K geometry within the basin-fill deposits Model retains flexibility and can honor geologic variability while minimizing the number of model parameters/model complexity Dacite dome Basin fill Granitic basement masked Arkosic fan Granite
Groundwater Models Basement based on gravity modified by AEM Parameter zones based on AEM resistivity zones mapped to grid Relative values used for hydraulic conductivity Section Along Row 71
California Desert Basins Tracy Nishikawa, Dave O Leary, Vicki Langenheim, Allen Christensen, and others Gravity for depth to basement A A
DATA SUBJECT TO REVISION Seismic Data in Joshua Tree Area -ties with borehole resistivity SEISMIC LINE Proposed WWTP Boundary YVUZ-5 La Contenta Road Sunnyslope Road?? Feature A???? N SEISMIC LINE Feature B
Recharge monitoring with gravity Jeff Kennedy Time-lapse gravity data can be used for monitoring and modeling artificial recharge through a thick unsaturated zone Gravity methods provide data to track recharge without the cost and regulatory requirements of monitoring wells, and to develop better models. Stationary, continuously-recording gravity meters Portable gravity meters and GPS
Recharge monitoring with gravity Jeff Kennedy Gravity measures aquifer storage change using sensors on the land surface A recent project in Arizona used gravity to track groundwater at an artificial recharge facility with spreading basins. There are two main applications: Spatial maps of gravity/storage change, shown here Continuous data Map showing the change in gravity after one month of basin drying. Gravity data reveal that the greatest decrease in storage is to the east, toward withdrawal pumps. Storage accumulates to the east.
Gravity and Groundwater Modeling In response to head changes in an unconfined aquifer, gravity data behave as spatially low-pass filtered head data the greater the depth to water, the heavier the filter. Importantly, unlike water level data, gravity data provide information about unsaturated-zone properties: initial, saturated, and residual water content. Gravity can be predicted directly from a groundwater flow model unlike every other geophysical method, no additional parameters are needed.
Central Valley, CA Claudia Faunt, Michelle Sneed, Jon Traum and others The recent drought, land-use changes, and restrictions on surface-water flows have resulted in extensive pumping, large groundwater-level declines, widespread land subsidence, and salinity issues
How is subsidence measured? Spirit Leveling Bench Mark Surveys Campaign GPS InSAR/PSInSAR Extensometer Tripod LiDAR Airborne LiDAR Continuous GPS
Subsidence Observations GPS Surveys Continuous GPS 27 sites on valley floor InSAR and LiDAR Used as calibration targets for modeling
Geophysical Methods and Groundwater Models Define Geologic Framework Model Model Layers Hydraulic Properties Water levels and storage Observations for Calibration Subsidence Water Levels Water Quality Seawater Intrusion